The young man was admiring his haircut in the mirror at a popular Dorchester barbershop, when a gunman stepped inside and opened fire, killing him.

The shooter did not say a word as he fired three or four rounds about 7 p.m. Thursday, striking the 20-year-old client, who had his back to the door, in the head. Police believe the victim, who died on the spot, was targeted.

A woman getting her hair styled was injured when a bullet shattered a display and glass fragments sliced her arm. She was treated at Boston ­Medical Center and later released.

The slaying, recounted Friday by the owner of Universal Barber Shop & Beauty Salon, sent feelings of shock across Geneva Avenue, a stretch of Dorchester known for sporadic violence.

“We’re feeling a lot of fear right now,” said Ovidio Rojas, the barbershop owner. “But there is nothing we can do.”

The shooting was a rude awakening after “a pretty quiet summer,” said the Rev. Jack ­Ahern of St. Peter Church on Bowdoin Street. Tensions in the community had been rising in the last month, he said.

“The scary thing is, it’s a public place,” Ahern said. “When it’s a drive-by, that’s tragic enough, but when you go into a business like that, you should feel at least somewhat secure. This really raises the level of concern.”

Rojas said that he was not inside the shop at the time of the shooting, but his wife, Miguelina, and their 12-year-old son were there, along with three barbers, three stylists, and their clients.

The victim, a regular customer, was sitting in a chair facing the shop’s front door, Rojas said. When barbers and stylists heard the first shot, they dropped to the floor. Miguelina Rojas said she grabbed her son to make sure he was safe.

“I’m in shock,’’ she said.

Police did not release the names of the victims and gave few details about the shooting. They said they did not want to provide a potential motive for the crime or a description of the suspect, for fear of compromising the investigation. They also could not say whether the shooter was acting alone, but they believed the male victim was the target of the crime.

Rojas said he hired a company to clean the blood and debris from the shooting. As the start of the work day dawned Friday, there was little sign of the killing that had occurred just over 12 hours before.

The sullied linoleum tiles were removed, the barber chair was gone, and the red, white, and blue barber pole continued to spin in the windowfront.

But there was one vestige of the fatal shooting that rocked this block of Geneva Avenue Thursday night: A bullet had pierced a hair product display case, leaving a spiderweb of cracked glass and a pool of liquid from an exploded bottle of conditioner.

Rojas said police had not given him any information about the investigation, but he did not see much reason to keep his doors closed. By noon, the barber shop ran as usual, and most chairs were occupied with clients getting trims, line-ups, or waiting. A few passersby stopped to stare in the window.

Rojas, who opened the shop 20 years ago, said he is aware of the violence in the neighborhood, but that he never thought it would be brought inside his establishment.

“It’s usually pretty safe right here,” Rojas said.

Since the shooting, he said he is considering installing ­security cameras.

This was not the first barbershop shooting in recent years. In September 2010, a man was seriously wounded at a Tremont Street barbershop in ­Roxbury when he was shot in the face as he waited to get a haircut.

Thursday’s slaying was the first fatal shooting on Geneva Avenue this year, according to a police spokeswoman.

The incident was the latest in a recent spate of violent crime in the area. On Tuesday, a man was shot several times just before 4 p.m. on Geneva and Blue Hill avenues and was hospitalized.

Laidy Fernandez, 18, works in the cafe next to the barbershop. She was not in the store at the time of Thursday’s shooting, but co-workers talked about their horror when they heard the “pow-pow-pow” of gunshots.

The shooting leaves her feeling terrified, but she is not sure what else she and other ­employees can do to keep themselves safe.

“There are already cameras up,” Fernandez said. “And we can’t lock the front doors. How would people get inside?”

Martine Powers can be reached at mpowers@globe.com. Follow her on Twitter @martine­powers. Meghan Irons can be reached at mirons@globe.com. Follow her on Twitter @meghanirons.